Project description:The emergence of SARS-CoV-2 variants and drug-resistant mutants necessitates additional antivirals. SARS-CoV-2 NSP14 N7-guanosine methyltransferase is responsible for viral RNA capping, facilitating replication and evading immune detection. NSP14 has emerged as a promising drug target, but the role of NSP14 in host-virus crosstalk and the cellular effects of NSP14 inhibition are poorly understood. Here, we performed structure-based virtual screen to identify non-nucleoside inhibitors targeting NSP14 SAM-binding pocket. Hit to Lead optimization resulted in the development of C10 that potently inhibited SARS-CoV-2 and variants with the EC50 values from 64.03 to 301.9 nM, comparable to FDA-approved drug remdesivir in our cell-based model. C10 is a selective inhibitor of β-coronavirus NSP14 and directly suppresses SARS-CoV-2 replication, as demonstrated by a SARS-CoV-2 replicon system. C10 specifically reversed NSP14-mediated host transcriptome alterations and, phenotypically, restored host cell cycle progression disrupted by NSP14. The antiviral efficacy of C10 was further validated in a transgenic mouse model of SARS-CoV-2 infection. Our findings indicate C10 holds promise for developing effective treatments against SARS-CoV-2 and emerging variants, as well as uncover a novel pathogenic role of NSP14 beyond its function in viral RNA capping, which may be also adaptable to other viral capping methyltransferase.
Project description:SARS-CoV-2 virus mimics host mRNA by capping its viral RNA to promote replication and evade host immune sensing. SARS-CoV-2 NSP14 is the N7-guanosine methyltransferase (N7-MTase) responsible for RNA cap-0 formation. Targeting NSP14 for antiviral drug development is an under-explored but promising strategy. Here we conducted a high-throughput screening on natural products library derived from Chinese herbal medicine to discover Emodin as a SARS-CoV-2 NSP14 inhibitor. Exploring Emodin derivatives, Questin was identified with potent cellular inhibitory activity (EC50=249 nM) against SARS-CoV-2, which inhibits NSP14 in an RNA cap competitive manner, making it one the most potent anti-coronaviral natural products. Mechanistically, besides catalyzing viral RNA capping, NSP14 by itself could remodel host transcriptome such as enriching CREBBP, a key host factor in cellular cyclic AMP response pathway, to promote viral infection. As a result, targeting NSP14 by Questin significantly impairs viral Replication & Translation step and reverses host transcriptome remodeled by NSP14. We next validated Questin as a promising lead with significantly improved toxicity upon acute exposure in zebrafish larvae. Taken together, our study not only demonstrates Questin as a potent drug lead for clinical antiviral application, but also highlights multiple antiviral potentials of NSP14 as therapeutic target.
Project description:The emergence of SARS-CoV-2 variants and drug-resistant mutants underscores the urgent need for novel antiviral therapeutics. SARS-CoV-2 NSP14, an N7-guanosine methyltransferase, plays a critical role in viral RNA capping, enabling viral replication and immune evasion. While NSP14 has emerged as a promising drug target, its role in host-virus crosstalk and the cellular consequences of NSP14 inhibition remain poorly understood. Here, we present the identification and characterization of C10, a highly potent and selective first-in-class non-nucleoside inhibitor of the NSP14 S-adenosylmethionine (SAM)-binding pocket. C10 demonstrates robust antiviral activity against SARS-CoV-2, including its variants, with EC50 values ranging from 64.03 to 301.9 nM, comparable to the FDA-approved drug remdesivir in our cell-based assays. C10 also exhibits broad-spectrum activity against other betacoronaviruses and directly suppresses SARS-CoV-2 genomic replication. C10 specifically reversed NSP14-mediated alterations in host transcriptome and restored host cell cycle progression disrupted by NSP14. The antiviral efficacy of C10 was further validated in a transgenic mouse model of SARS-CoV-2 infection. Our findings highlight C10 as a promising candidate for the development of effective treatments against SARS-CoV-2 and its emerging variants. This study also uncovers a novel mechanism of NSP14 in SARS-CoV-2 pathogenesis and its therapeutic potential, providing insights that may extend to other viral capping methyltransferases.
Project description:SARS-CoV-2, the causative agent of COVID-19, manipulates host gene expression through multiple mechanisms, including disruption of RNA processing. Here, we identify a novel function of the viral nonstructural protein 14 (NSP14) in inducing N7-methylguanosine (m7G) modification in the internal sequences of host mRNA. We demonstrate that NSP14 catalyzes the conversion of guanosine triphosphate (GTP) to m7GTP, which is subsequently incorporated into mRNA by RNA polymerase II, resulting in widespread internal m7G modification. This activity is dependent on NSP14's N7-methyltransferase (N7-MTase) domain and is enhanced by interaction with NSP10. Internal m7G modification by NSP14 predominantly occurs in the nucleus and is conserved across alpha-, beta- and gamma-coronaviruses. Mechanistically, we show that this RNA modification disrupts normal splicing by promoting intron retention and generating novel splice junctions. Importantly, inhibition of m7G modification, through pharmacological targeting of NSP14 or RNA polymerase II, impairs SARS-CoV-2 replication, indicating that the virus hijacks host transcriptomic machinery to support infection. Our findings reveal a previously unrecognized epitranscriptomic mechanism by which coronaviruses reprogram host gene expression and suggest that NSP14-induced m7G modification is a potential therapeutic target.